Heat exchangers for warming physiological solutions are known. One such heat exchanger is disclosed in U.S. Pat. Nos. 4,759,749 and 4,878,537, both assigned to the assignee of the instant invention. The heat exchanger disclosed in the '749 and '537 patents has an outer conduit covering an inner conduit that is made of aluminum. End caps seal the outer conduit. A through channel is provided by the inner conduit and another flow channel is provided between the outer wall of the inner conduit and the inner wall of the outer conduit. The outer wall of the inner conduit has a spiral configuration so that the infusate that is to be heated would follow the spiral path established between the outer wall of the inner conduit and the inner wall of the outer conduit. The infusate is therefore heated by convection from the wall of the inner conduit. This heat exchanger works well. However, due to the fact that the inner conduit is made of aluminum, the cost of manufacturing the heat exchanger is relatively high. Moreover, a multi-step manufacturing process is required to effect a spiraled path at the outer wall of the inner conduit and the fitting of the inner conduit to the outer conduit, and to ensure that there is a flow channel established between the outer spiraled wall of the inner conduit and the inner wall of the outer conduit. Furthermore, given that only the inner conduit is heated by the heated water from the heater, the infusate is only convectively heated by the heat at the outer wall of the inner conduit, while at the same time heat loss occurs due to the infusate contacting the inner wall of the outer conduit which is exposed to atmosphere.